Abstract
Color, motion direction, and orientation are incontrovertible basic feature dimensions, since dimensional singletons, eg a red item among green ones, attract attention automatically. The ocularity dimension
is defined as the signed difference in input strengths from left and right eyes associated with an item. I recently showed that eye-of-origin singletons, which are ocularity extrema, eg an item shown to the
left eye among many items to the right eye, capture attention automatically, indeed more strongly than an orientation singleton with orientation contrast 50° [Zhaoping, 2008
Journal of Vision 8 (5):1, 1-18]. This suggests that ocularity is a strong basic feature dimension, hitherto overlooked because of its transparency to awareness. Here, I report that ocularity singletons of all sorts, ie, items with unique ocularities among background items of uniform ocularity, also attract attention, as manifested by their exogenous cueing effect, eg a difficult visual search becomes easier when the target is also an ocular
singleton. In particular, a unique monocular item pops out among binocular ones, or a unique binocular item among those shown to a single eye. Further, as the only item with unbalanced inputs to the two eyes, an ocular singleton that is neither nearest nor farthest in depth, can pop out from background items at various depths.
